No doubt people who are tired or drowsy are more likely to run through a red light than people who are rested and alert. But does that mean local governments should have the power to order people when to go to bed and get up, because their tiredness can have an effect on the likelihood of their driving through a red light? The power to regulate indirect effects is not a slippery slope. It is the disastrous loss of freedom that lies at the bottom of a slippery slope.